<!DOCTYPE html>
<html lang="zh-CN">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    // console.log(1 + 1);
    // console.log(1 * 1);
    // console.log(1 / 1);
    // console.log(5 % 3);

    // let r = prompt('请输入圆的半径：')
    // let re = 3.14 * r * r
    // document.write(re)

    // console.log('你好' - 3); //NaN = not a number

    // console.log(NaN + 2);
    // console.log(NaN / 2);
    // console.log(NaN - 2);
    // console.log(NaN * 2);
    // console.log(NaN % 2);

    console.log(NaN === NaN);

  </script>
</body>

</html>